1. Field of the Invention
The invention is related to a steel sheet and a fabrication method thereof, and more particularly, to a steel sheet containing a zinc alloy coating layer on a surface thereof and a fabrication method thereof.
2. Description of Related Art
Iron and steel materials are currently one of the most commonly used industrial materials. To improve corrosion resistance of iron and steel workpieces, one known method includes forming a coating layer on a surface of an iron-based material, such as forming a layer of metal zinc with an electroplating method or a hot-dip coaling method. There are two principles of corrosion prevention for a galvanized coating layer. The first isolates contact between the iron-based material and the environment by covering the iron-based material to achieve corrosion prevention, and the second achieves corrosion prevention through the so-called “sacrificial anode protection method.” Specifically, a metal having a stronger ability of reduction is used as a guard electrode and connected to a protected metal to form a primary cell. A metal having stronger ability of reduction is used as the anode and is consumed due to an oxidation reaction, and the protected metal is used as the cathode, thereby preventing corrosion.
However, if a hot stamping pre-heat treatment is to be performed on a steel sheet having a metal nickel coating layer on a surface thereof, the high temperature of the preheating step of the hot stamping significantly oxidizes the metal zinc, such that the effective content of metal zinc capable of providing a protective effect is reduced. At the same time, the high temperature may also melt zinc such that liquid zinc penetrates through the grain boundary of iron, thereby causing intergranular damage during stamping, which is the so-called liquid metal induced embrittlement (LMIE) effect. Based on the above, the surface coating layer of iron and steel materials still requires further research.